Electric heater



Oct. l5, 1929. w. E. ADDlcKs ELEGTRI C HEATER Filed Feb. 11, 1924 ITIIIIIIIIII A TTORNEY Patented Oct. 15, 1929 UNITED STATES PATENT OFFICE WALTER E. ADDICKS, 0F NEW YORK, N. Y., ASSIGNOR, BY MESNE ASSIGNMENTS, TO CUTLER-HAMMER, INC., A CORPORATION 0F DELAWARE ELECTRIC HEATER Application led. February 11, 1924. Serial No. 691,892.

This invention relates to electric heaters and is particularly applicable to flat electric heaters including a resistor enclosed by and insulated from a sheet metal armor.

Heaters of the aforesaid character are commonly provided with insulating strips for supporting the resistor and for insulating the same from the armor. Heretofore the construction of such heaters rendered it necessary to employ insulating strips which were adapted to maintain their mechanical strength under the temperatures encountered in operation. The insulating strips usually employed were made up of mica laminations held together by an inorganic binder of such character as to be unaffected by relatively high temperatures.

The present invention has among its obj ects to provide a heater of such construction 'as to permit the employment of insulating strips consisting of mica laminations held together by an organic binder capable of being oxidized by heat treatment for complete removal thereof.

Another object is to construct the heater so that access of air to the insulating strips is permitted during the heat treatment to facilitate oxidation of the binder.

Another object is to facilitate manufacture of the heater by supporting the insulation strips to prevent displacement of the laminations thereof after removal of the binder.

Another object is to increase the rigidity of the heater and to overcome any tendency toward bowing or deflection thereof due to unequal expansion of the armor.

Various other objects and advantages of the invention will hereinafter appear.

The accompanying drawing illustrates an embodiment of the invention which will now be described, it being understood that the embodiment illustrated can be modified in certain respects without departing from the scope of the appended claims.

In the drawing,

Figure 1 is a plan view of a heater embodying the invention, a portion thereof being broken away;

Fig. 2 is a fragmentary view of certain of the parts of the heater shown in Fig. 1;

Fig. 3 is a sectional view of one end of the heater, and

Fig. 4 is a sectional view on line 4-4 of Fig. 8.

The heater illustrated in the drawing includes a resistor 1 wound upon an insulating strip 2, pressure plat-es 3 and 4 arranged on opposite sides of said resistor and insulated therefrom by mica strips 5 and 6, and a sheet metal channel 7 having its opposite sides folded over the pressure plates 3 and 4. The opposite ends of pressure plates 3 and 4 project beyond the ends of channel 7 and such projecting ends are each provided with an insulated terminal eyelet 8 connected to the resistor 1 and an insulated supporting eyelet 9. As hereinafter set forth, the insulating strips 2, 5 and 6 are made up of mica laminations held together by an organic binder, such as shellac, and during the construction of the heater such strips are subjected to heat treatment to oxidize the carbon content of the binder.

As before stated, the resistor 1 is wound upon an insulating strip 2, and as shown in Figs. 2 and 3, the opposite ends of said refsistor are passed through openings at points adjacent the opposite ends of the winding strip 2 and each end is brought outwardly below a terminal plate 10 and upwardly through an opening 11 in such plate, which opening is adapted to receive the eyelet 8. Each of the terminal plates 10 has a pair of mica insulating plates 12 and 13 arranged on opposite sides thereof and said insulating plates and the terminal plates are secured to the winding strip 2 by hollow rivets 14. After assembly of the aforedescribed terminal parts on the winding strip 2 the strip of mica insulation 5 is wrapped around the resister, the opposite sides of said strip being arranged in overlapping relation, as shown in Fig. 4. Also, it should be noted from Fig. 2 that the strip 5 overlaps the insulating plates 12 and 13 and that such plates are ot' greater width than the winding strip whereby an air space is provided around the winding strip 2 and the resistor 1 mounted thereon. It will be noted from Fig. 4 that due to overlapping of the sides of strip 5 a double thickness of mica is provided on the upper side of the winding strip 2 and an equal thickness of mica on the underside of said winding stripv by strip 6.

As before stated, pressure plates 3 and 4E are provided with a terminal eyelet 8 and a supporting eyelet 9 on opposite ends thereof, and, as shown in Fig. 3, said plates are provided with enlarged openings for receiving said eyelets. Eyelets 8 and 9 are held in centered relation with respect to said openings by insulating washers 15 of substantially the same thiclmess as said pressure plates. rlhe opposite ends of the resistor 1 as before stated, extend upwardly through openings in the terminal plates 10 and as shown in Fig. 3 each end of said resistor is clamped between metal Washers 1G and 17 arranged on the upperside of pressure plate 3, the latter washer being insulated from said pressure plate by a mica washer 18. Fach of the eyelets 8 has one end riveted over the washer 16 while the opposite end thereof is riveted over a washer 19 insulated from pressure plate 4, by a mica washer 20. Each of the eyelets 9 has its upper side riveted over a metal washer 21 insulated from pressure plate 3 by a mica Washer 22 while the lower end of said eyelet is riveted over a metal washer 23 insulated from pressure plate i by a mica washer 274:.

As before stated, the strips 2, 5 and 6 are made up of mica laminations held together by a shellac binder adapted to be oxidized by heattreatment. In manufacturing the aforedescribed heater all the partsthereof are assembled with the exception of the channel 7 and the heater is then placed in an oven and baked at a temperature sul'hciently high and for a time sufliciently long' to carbonize the binder and ultimately oXidiZe the carbon to drive it off entirely. The result of this baking.

operation is to'reduce all of the mica content of the insulating strips to clear mica laminations with no binder whatever holding` the laminations together. lt should be noted that during the baking operation the unfastened edges of the pressure plates permits free access yof air therebetween to facilitate oxidation of the binder and that when the Ybaking operation is completed Said plates serve to hold the mica laminations in place.

After the baking operation channel? is applied and'it is apparent that when the heater is completed the mica laminations are securely Vheld in place by the metal armor to prevent displacement thereof and such laminations offer better insulation than mica plate with any sort of inorganic' binder. Furthermore, it should be noted that the terminal leads of the resistor are held between two pressure plates and thus given substantial protection on Yboth sides. Also it is apparent that the heater is very rigid and since equal thicknesses of metal are provided on `both sides thereof any tendency toward bowing or defiection due to unequal expansion of the armor is overcome.

What I claim as new and desire to secure by Letters Patent is:

1. An electric heater comprising a pair of metallic strips held together at points adjacent opposite ends thereof by an insulated terminal rivet, a heater element arranged between said strips and having opposite ends thereof connected to said rivets, a mica insulating sheath surrounding said element and an elongated sheet metal member wrapped about said metallic strips to prevent separation thereof.

2. An lelectric heater comprising an insulated heater element, a pair of metallic strips arranged on opposite sides of said element and having their opposite ends projecting therebeyond, a pair of insulated supporting eyelets arranged on opposite ends of said strips and serving to clamp the same together and a pair of insulated terminal eyelets connected to said element and supported by said strips.

3. The processV of making an electrical heater which comprises arranging a resistance element within an insulating sheath consisting of mica laminations held together by an organic binder, holding said sheath and the resistance element therein between two metal pressure plates, subjecting the aforesaid parts to heat treatment to oxidize the binder in said sheath for complete removal thereof and thereafter assembling the aforesaid parts within a sheet metal armor.

1. rlhe process of making an electric heater which comprises enclosing` a resistance element within an insulating sheath, consisting of mica laminations held together by an organic binder, subjecting the aforesaid parts to heat treatment to oXidize the binder in said sheath for complete removal thereof, and providing a metallic armor about said sheath to prevent displacement of the laminations thereof after heat treatment.

5. rl`he process of making an electric heater which consists in winding a resistance wire about an insulating strip consisting of mica laminations held together by an organic binder, wrapping said strip and the resistance wire thereon within an insulating sheath, also consisting of mica laminations held together by an organic binder, arranging metal plates on opposite sides of said sheath to clamp the latter against said winding strip and the resistance wire thereon, baking the aforesaid parts to oXidize the'binder in said winding strip and said sheath for complete removal thereof, and thereafter wrapping a sheetmetal armor about said plates.

ln witness whereof, l have hereunto subscribed my name.

WALTER E. ADDICKS.' 

